Method and apparatus for manufacturing magnetoresistive element

ABSTRACT

The present invention relates to a method for manufacturing a magnetoresistive element having a magnetization pinned layer, a magnetization free layer, and a spacer layer including an insulating layer provided between the magnetization pinned layer and the magnetization free layer and current paths penetrating into the insulating layer. A process of forming the spacer layer in the method includes depositing a first metal layer forming the metal paths, depositing a second metal layer on the first metal layer, performing a pretreatment of irradiating the second metal layer with an ion beam or a RF plasma of a rare gas, and converting the second metal layer into the insulating layer by means of supplying an oxidation gas or a nitriding gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2004-233641, filed Aug. 10, 2004,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus formanufacturing a magnetoresistive element having a structure in which acurrent is supplied perpendicularly to the plane of the element.

2. Description of the Related Art

The performance of magnetic devices, particularly magnetic heads, hasbeen drastically improved by the discovery of the giant magnetoresistiveeffect (GMR). Specifically, application of a spin-valve film (SV film)to magnetic heads and magnetic random access memories (MRAMs) hasbrought about marked technical improvement in the field of magneticdevices.

The “spin-valve film” is a stacked film having a structure in which anonmagnetic metal spacer layer is sandwiched between two ferromagneticlayers. In the spin-valve film, the magnetization of one ferromagneticlayer (referred to as a “pinned layer” or “magnetization pinned layer”)is pinned by an antiferromagnetic layer or the like, whereas themagnetization of the other ferromagnetic layer (referred to as a “freelayer” or “magnetization free layer”) is made rotatable in accordancewith an external field (for example, a media field). In the spin-valvefilm, a giant magnetoresistace change can be produced by a change of therelative angle between the magnetization directions of the pinned layerand the free layer.

Conventional spin-valve films are current-in-plane (CIP)-GMR elements inwhich a sense current is supplied parallel to the plane of the element.In recent years, much attention has been paid tocurrent-perpendicular-to-plane (CPP)-GMR elements in which a sensecurrent is supplied substantially perpendicular to the plane of theelement because the CPP-GMR elements exhibit a greater GMR effect thanthe CIP-GMR elements.

When such a magnetoresistive element is applied to a magnetic head, ahigher element resistance poses problems in regard to shot noise andhigh frequency response. It is appropriate to evaluate the elementresistance in terms of RA (a product of the resistance and the area).Specifically, RA must be several hundred Ωμm² to 1 Ωμm² at a recordingdensity of 200 Gbpsi (gigabits per square inch) and less than 500 Ωμm²at a recording density of 500 Gbpsi.

In connection with these requirements, the CPP element has a potentialto provide a high MR ratio even though it exhibits a low resistance on atrend of increasingly reducing the size of the magnetic device. Underthe circumstances, the CPP element and the magnetic head using the sameare expected to be promising candidates to achieve a recording densityof 200 Gbpsi to 1 Tbpsi (terabits per square inch).

However, a metal CPP element in which the pinned layer, the spacer layerand the free layer (this three-layer structure is referred to as aspin-dependent scattering unit) are made of metal exhibits only a lowresistance change rate. Accordingly, the metal CCP element isinsufficient to sense very weak fields resulting from an increaseddensity and is thus hard to put to practical use.

To solve this problem, a CPP element has been proposed which uses, as anonmagnetic spacer layer, a nano-oxide layer (NOL) containing currentpaths extending across the thickness of the element (see, for example,Jpn. Pat. Appln. KOKAI Publication No. 2002-208744). Such a CPP elementcan increase both the element resistance and the MR ratio due to acurrent-confined-path (CCP) effect. Such an element is referred to as aCCP-CPP element hereinafter. Incidentally, a method for forming a layermainly composed of an oxide in a magnetoresistive element has alreadybeen proposed (see Jpn. Pat. Appln. KOKAI Publication No. 2002-76473).

Compared to the metal CPP element, the CCP-CPP element has the followingimprovement effect. A metal CPP element was produced which had thestructure of substrate/Ta [5 nm]/Ru [2 nm]/PtMn [15 nm]/Co₉₀Fe₁₀ [4nm]/Ru [0.9 nm]/Co₉₀Fe₁₀ [4 nm]/Cu [5 nm]/Co₉₀Fe₁₀ [1 nm]/Ni₈₁Fe₁₉ [3nm]/Cu [1 nm]/Ta cap layer. Ordering heat treatment for pinning thepinned layer by PtMn was carried out in a magnetic field at 270° C. for10 hours. On the other hand, a CCP-CPP element having, as a spacerlayer, a NOL formed by naturally oxidizing Al₉₀Cu₁₀ [0.7 nm], instead ofthe Cu spacer layer in the metal CPP element, was produced. The arearesistances RA, the changes of the area resistance ΔRA, and MR ratios ofthese elements are shown below.

metal CPP CCP-CPP RA  100 mΩμm²  370 mΩμm² ΔRA  0.5 mΩμm²  5.6 mΩμm² MRratio 0.5% 1.5%

As described above, the CCP-CPP element exhibits an improved MR ratioand an improved RA and thus has ΔRA one order of magnitude higher thanthe metal CPP element.

However, in spite of their good characteristics shown above, the CCP-CPPelement is supposed insufficient to sense very weak field signals from amedia with a high recording density of 200 to 500 Gbpsi. A trialcalculation indicates that the MR ratio must be at least 3% at, forexample, a recording density of 200 Gbpsi and RA of 500 mΩμm². In orderto obtain a sufficient signal-to-noise ratio, it is necessary to providean MR ratio of at least 7%, that is, at least double the trialcalculation. In view of these indices, the above value of the MR ratiois about half the required specification. Thus, it is difficult to putthese elements to practical use.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided amethod for manufacturing a magnetoresistive element comprising amagnetization pinned layer a magnetization direction of which issubstantially pinned in one direction, a magnetization free layer amagnetization direction of which varies depending on an external field,and a spacer layer including an insulating layer provided between themagnetization pinned layer and the magnetization free layer and currentpaths penetrating into the insulating layer, the method comprising:depositing a second metal layer on a first metal layer; and causing thefirst metal layer to penetrate into the second metal layer as the metalpaths and converting the second metal layer into the insulating layer bymeans of supplying an oxidation gas or a nitriding gas.

In the method according to an aspect of the present invention mayfurther comprise: performing a pretreatment of irradiating the secondmetal layer with an ion beam or a RF plasma of a rare gas prior to theconverting step.

According to another aspect of the present invention, there is provideda method for manufacturing a magnetoresistive element comprising amagnetization pinned layer a magnetization direction of which issubstantially pinned in one direction, a magnetization free layer amagnetization direction of which varies depending on an external field,and a spacer layer including an insulating layer provided between themagnetization pinned layer and the magnetization free layer and currentpaths penetrating into the insulating layer, the method comprising aprocess of forming the spacer layer comprising: depositing a first metallayer forming the metal paths; depositing a second metal layer on thefirst metal layer; performing a pretreatment of irradiating the secondmetal layer with an ion beam or a RF plasma of a rare gas; andconverting the second metal layer into the insulating layer by means ofsupplying an oxidation gas or a nitriding gas.

According to still another aspect of the present invention, there isprovided an apparatus for manufacturing a magnetoresistive element usingthe above method, the apparatus comprising: a load lock chamber to whicha substrate is loaded; a depositing chamber in which a metal layer isdeposited on the substrate; a reaction chamber comprising a suppliersupplying an oxidation gas or a nitriding gas and an ion source whichexcites a rare gas to generate plasma and irradiates the metal layerwith an ion beam; and a substrate transfer chamber connected to thechambers via vacuum valves.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view of a CCP-CPP element according to anembodiment of the present invention;

FIGS. 2A to 2D are cross-sectional views schematically illustrating amethod for manufacturing the CCP-CPP element according to the embodimentof the present embodiment;

FIG. 3 is a diagram schematically showing the configuration of anapparatus used to manufacture the CCP-CPP element according to theembodiment of the present embodiment;

FIG. 4 is a schematic diagram showing an example of the oxidationchamber in FIG. 3;

FIG. 5 is a schematic diagram of an example of the ion source in FIG. 4;

FIG. 6 is a perspective view of a CCP-CPP element according to Example1;

FIG. 7 is a graph showing the relationship between the RA and the MRratio of a CCP-CPP element manufactured according to Example 2;

FIG. 8 is a graph showing an R-H loop of the CCP-CPP element accordingto Example 2;

FIGS. 9A to 9C are a perspective view of the CCP-CPP element accordingto Example 2, an enlarged perspective view of a current path, and anequivalent circuit diagram of the CCP-CPP element;

FIGS. 10A and 10B are graphs showing the I-V and R-V characteristics ofthe CCP-CPP element according to Example 2;

FIGS. 11A and 11B are graphs showing the I-V and R-V characteristics ofan element similar to a TMR element produced for comparison with Example2;

FIG. 12 is a graph showing the relationship between the RA and the MRratio of a CCP-CPP element according to Example 3;

FIG. 13 is a cross-sectional view of a magnetic head according to anembodiment of the present invention;

FIG. 14 is a cross-sectional view of a magnetic head according to anembodiment of the present invention;

FIG. 15 is a perspective view of a magnetic recording apparatusaccording to an embodiment of the present invention;

FIG. 16 is a perspective view of a magnetic head assembly according toan embodiment of the present invention;

FIG. 17 is a diagram showing an example of the matrix configuration of amagnetic memory according to an embodiment of the present invention;

FIG. 18 is a diagram showing another example of the matrix configurationof a magnetic memory according to an embodiment of the presentinvention;

FIG. 19 is a cross-sectional view showing a major portion of a magneticmemory according to an embodiment of the present invention; and

FIG. 20 is a cross-sectional view of the magnetic memory taken along theline A-A′ in FIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional view of a magnetoresistive element(CCP-CPP element) according to an embodiment of the present invention.The magnetoresistive element shown in FIG. 1 has a lower electrode 11,an underlayer 12, a pinning layer 13, a pinned layer 14, a metal layer15, a spacer layer (CCP-NOL) 16, a metal layer 17, a free layer 18, acap layer 19, and an upper electrode 20; all these layers are formed ona substrate (not shown). The spacer layer (CCP-NOL) 16 includes aninsulating layer 22 and current paths 21 penetrating the insulatinglayer 22.

With reference to FIGS. 2A to 2D, of a method for manufacturing themagnetoresistive element (CCP-CPP element) according to the embodimentof the present invention will be briefly described. Here, an example inwhich the spacer layer 16 including the current paths 21 made of Cu areformed in the insulating layer 22 made of Al₂O₃ will be described.

As shown in FIG. 2A, a lower electrode, an underlayer, and a pinninglayer (these members are not shown) are formed on a substrate, and thena pinned layer 14 is deposited on the pinning layer. A first metal layerm1 (for example, Cu) that forms current paths is deposited on the pinnedlayer. A second metal layer m2 (for example, AlCu or Al) to be convertedinto an insulating layer is deposited on the first metal layer m1.

As shown in FIG. 2B, a pretreatment is performed by irradiating thesecond metal layer m2 with an ion beam of rare gas (for example, Ar).This pretreatment is referred to as a pre-ion treatment (PIT). The PITcauses the first metal layer m1 to be partly sucked up in the secondmetal layer m2 by which a part of m1 intrudes into m2.

As shown in FIG. 2C, an oxidation gas (for example, oxygen) is suppliedto oxidize the second metal layer m2. The oxidation converts the secondmetal layer m2 into an insulating layer 22 made of Al₂O₃, and also formscurrent paths 21 penetrating the insulating layer 22, thereby forming aspacer layer 16.

As shown in FIG. 2D, a metal layer 17 such as Cu is deposited on thespacer layer 16, and a free layer 18 is deposited on the metal layer 17.The metal layer 17 on the spacer layer 16 has a function for preventingthe free layer, formed on the metal layer, from being affected byoxidation and a function of improving crystallinity of the free layer.For example, when the insulating layer 22 is formed of amorphous Al₂O₃,the crystallinity of the metal layer formed thereon tends to bedegraded. However, if a layer having a function of improving thecrystallinity of the free layer such as a Cu layer is provided on theinsulating layer 22, even if the thickness of the Cu layer is onlyseveral angstrom, the crystallinity of the free layer would besignificantly improved. It should be noted that the metal layer 17 neednot necessarily be provided in some cases depending on the materials ofthe spacer layer 16 and the free layer 18.

The method according to the embodiment of the present invention improvesthe purity of the current paths 21, which penetrate the insulating layer22 in the spacer layer 16. This in turn makes it possible to manufacturea magnetoresistive element with a high MR ratio without significantlyincreasing the area resistance RA.

The above processes will now be described in more detail.

In FIG. 2B, the pretreatment (PIT) is the most important andcharacteristic step in the method of the present invention; thepretreatment (PIT) is performed after the deposition of the first andsecond metal layers m1 and m2 on the pinned layer 14 and beforeoxidation, in order to allow a part of the first metal layer m1 tointrude into the second metal layer m2 to form current paths.

In the PIT process, the second metal layer m2 is irradiated with an ionbeam of rare gas; the second metal layer m2 is to be converted into theinsulating layer 22 in the spacer layer 16. The rare gas includes Ar,Kr, He, and Xe. Ar is most desirable in terms of manufacturing costs. Inplace of Ar, another rare gas having a larger mass such as Xe may beused as required to produce a specific effect.

Preferable conditions set for irradiation with an ion beam in the PITprocess are an acceleration voltage V+ of 30 to 130 V, a beam current Ibof 20 to 200 mA, and an RF power of 10 to 300 W, a RF power inducingplasma in an ion source in order to maintain the beam current at aconstant value. These conditions are significantly weaker than those forion beam etching. This is because marked etching during the PIT processmay eliminate the second metal layer (AlCu or Al) to be oxidized.

An alternative method is conceivable in which a second metal layer witha thickness larger than a desired thickness is deposited taking thethickness of an etched part of 20 Å or more into account, followed byperforming an ion beam treatment under conditions more intensive thanthose described above to leave a partly etched second metal layer havingthe desired thickness. However, this method is not so preferable. Thisis because the intensive conditions for the ion beam treatment makeuniform control difficult to vary etching across the thickness of themetal film depending on a position in the film surface, thus possiblydamaging the pinned layer. The main purpose of the PIT treatment isabsolutely to cause suction of the metal layer m1. Thus, decrease in thethickness of the metal layer m2 is a very small amount with a typicalvalue of 0 to 3 Å, which is different from the case of etching.

The incident angle of the ion beam is varied between 0 and 80°; theincident angle is defined to be 0° when the beam is perpendicular to thefilm surface upon incidence and to be 90° when the beam is parallel tothe film surface upon incidence. The treatment time required for the PITprocess is preferably about 15 to 180 seconds and more preferably 30seconds or more in terms of controllability and the like. A longertreatment time is not preferable because it degrades the productivityfor the CCP-CPP element. In these regards, the treatment time is mostpreferably with in a range between about 30 and 180 seconds.

As shown in FIG. 2B, the PIT process causes the Cu of the first metallayer to be sucked up in the second metal layer by which Cu intrudesinto the second metal layer. The Cu of the first metal layer has aprotruded shape penetrating into the second metal layer, which remainsas a metal layer without being converted into an insulation layer afterthe later oxidation treatment and forms current paths. As describedabove, the second metal layer may be AlCu or Al. If an AlCu alloy isused as a second metal layer, not only suction of Cu of the first metallayer but also a phase separation phenomenon occurs, resulting inseparation of Al and Cu from the AlCu alloy. If Al free from Cu is usedas a second metal layer, only suction of Cu of the first metal layeroccurs. In this manner, the PIT process causes Cu of the first metallayer to be sucked up in the second metal layer. Accordingly, a metalother than Al can be used for the second metal layer. The second metallayer may be, for example, Si, Hf, Zr, Mg, W, Mo, Nb, Cr, Ti, or analloy containing these elements, which is easily converted into a stableoxide. Thus, the PIT process, that is a type of energy treatment,enables the first metal layer to be sucked up in the second metal layer.

As shown in FIG. 2C, an oxidation treatment is performed after PIT. Thisprocess utilizes a difference in oxidation energy that Al is readilyoxidized but Cu is not. Thus, a spacer layer is formed in which Cuforming the current paths is separated from the insulating layer ofAl₂O₃. The oxidation method may be natural oxidation or a methodsupplying an oxidation gas (for example, oxygen) while irradiating withan ion beam of rare gas. The latter method is more preferable and isreferred to as ion beam-assisted oxidation (IAO). The rare gas includesAr, Xe, Kr, and He.

Preferable conditions set for irradiation with an ion beam in the IAOprocess are an acceleration voltage V+ of 40 to 200 V, a beam current Ibof 30 to 200 mA, and an RF power of 20 to 400 W, the RF power inducingplasma in an ion source in order to maintain the beam current at aconstant value. The IAO treatment time is preferably about 15 to 300seconds and more preferably about 20 to 180 seconds. The treatment timeis reduced when a stronger ion beam is used and increased when a weakerion beam is used.

The preferable range of the amount of oxygen exposure during oxidationis 1,000 to 5,000 L (1 L=1×10⁻⁶ Torr×sec) for IAO, and 3,000 to 30,000 Lfor natural oxidation. The oxygen exposure amount for IAO can becalculated on the basis of change in the degree of vacuum in anoxidation chamber which occurs when oxygen gas at a predetermined flowrate is allowed to flow the oxidation chamber without introducing gassuch as Ar. For example, if the degree of vacuum is 1×10⁻⁴ Torr and theoxidation time is 30 sec, it is calculated as (1×10⁻⁴ Torr×30sec)/(1×10⁻⁶ Torr ×sec)=3,000 L. An actual IAO process uses Ar gas foran ion beam or Ar gas for an electron emitter. Although the change inthe degree of vacuum in this case is different from that indicated on avacuum gauge when only oxygen gas is allowed to flow, the oxygenexposure amount under a certain oxygen partial pressure can becalculated as described above.

The IAO process is expected to produce the effect described below. Forexample, during the PIT process, the first metal may insufficientlyintrude into the second metal layer, resulting in inappropriateformation of the current paths. In addition, when AlCu is used as asecond metal layer, the PIT process may incompletely separate the secondmetal layer into Al and Cu. Even if such a phenomenon is caused, IAO cancompensate for an insufficiently separated state between Al and Cuduring the PIT process. In addition, with the IAO process, irradiationwith a rare-gas ion beam, i.e., Ar ion beam, in an oxygen atmosphereenables reduction to occur together with oxidation. That is, Al, whichis easily oxidized, is oxidized by the energy assistance effect of theAr ion beam. However, Cu, which is more difficult to oxidize than Al, ishindered from being oxidized and is reduced by the energy assistanceeffect of the Ar ion beam. This facilitates the migration of oxygen toAl, i.e., oxidation of Al, which is readily oxidized. As a result,highly pure Cu current paths can be generated. As described later, theimprovement of purity of the current paths is important in achieving ahigh MR ratio based on a physical principle of CCP element. Accordingly,a high MR ratio can be realized by suppressing the oxidation of thecurrent paths.

FIG. 3 schematically shows the configuration of an apparatus used tomanufacture the magnetoresistive element (CCP-CPP element) according tothe embodiment of the present invention. As shown in FIG. 3, thefollowing are provided around a transfer chamber (TC) via vacuum valves:a load lock chamber 51, a pre-cleaning chamber 52, a first metaldeposition chamber (MC1) 53, a second metal deposition chamber (MC2) 54,and an oxidation chamber (OC) 60. In this apparatus, a substrate can betransferred in vacuum between the chambers, connected together via thevacuum valve. This enables the surface of the substrate to be keptclean.

The method described below is used to manufacture the CCP-CPP elementaccording to the embodiment of the present invention using the apparatusshown in FIG. 3. A substrate is loaded into the load lock chamber 51 andthen transferred via the transfer chamber 50 through the pre-cleaningchamber 52 to the first metal deposition chamber 53 or second metaldeposition chamber 54 in a predetermined order. In these metaldeposition chambers, the underlayer 12, the pinning layer 13, the pinnedlayer 14, a first metal layer forming the current paths in the spacerlayer 16, and further a second metal layer to be converted into theinsulating layer in the spacer layer 16 are deposited on the substratehaving the lower electrode 11. Then, the substrate is transferred to theoxidation chamber 60, where a pretreatment (PIT) and an oxidationtreatment (IAO) are performed to form a spacer layer 16 as describedabove. Since the PIT process does not use any oxygen gas, it can beperformed in a metal deposition chamber. After the oxidation treatment,the substrate is transferred via the transfer chamber 50 to the firstmetal deposition chamber 53 or second deposition chamber 54 in apredetermined order. Thus, the metal layer 17, the free layer 18, thecap layer 19, and an upper electrode 20 are deposited above the spacerlayer 16.

FIG. 4 schematically shows an example of the oxidation chamber 60 inFIG. 3. As shown in FIG. 4, the oxidation chamber 60 is evacuated by avacuum pump 61. Oxygen gas is introduced into the oxidation chamber 60through an oxygen conduit 62; the flow rate of the oxygen gas iscontrolled by a mass flow controller (MFC) 63. An ion source 70 isprovided in the oxidation chamber 60. Types of the ion source include aninductive coupled plasma (ICP) type, a capacitive coupled plasma type,an electron-cyclotron resonance (ECR) type, and a Kauffman type. For theprocess according to the present invention, the ICP type is desirable,among the above ion source types, because plasma can desirably begenerated in an area with low plasma energy (low plasma potential). TheICP type may be modified by, for example, placing a permanent magnetaround the ion source in order to enable plasma to be generated with alow RF power. A substrate holder 80 and a substrate 1 are arrangedopposite the ion source 70. Three grids 71, 72, and 73 are provided atan ion emission port of the ion source 70 to adjust ion acceleration. Aneutralizer 74 is provided outside the ion source 70 to neutralize ions.The substrate holder 80 is supported so as to be freely tilted. Theangle at which ions are incident on the substrate 1 can be varied over awide range. A typical incident angle ranges between 15 and 60°.

In the oxidation chamber 60, the PIT process can be performed byirradiating the substrate 1 with an ion beam such as Ar, and the IAOprocess can be performed by irradiating the substrate 1 with an ion beamsuch as Ar while supplying the chamber 60 with oxygen from the oxygenconduit 62.

As described above, with the method according to the present invention,it is important to stably generate plasma with a low power in order toperform the PIT and IAO processes under moderate conditions. Thus, theusage and structure of the ion source will be described in detail withreference to FIG. 5.

FIG. 5 is a diagram showing the ion source 70 in FIG. 4 in detail. An Argas, for example, is introduced into the ion source 70. A plasmaexcitation source 75 is used to generate plasma in the ion source 70.Three grids, a positive (V+) grid, a negative (V−) grid 72, and a ground(GND) grid 73 are arranged at the front surface (ion emission port) ofthe ion source 70. Such three grids are preferably used to facilitatefocusing in order to improve distribution in the film surface. In thiscase, the negative grid is used for focusing. Such three grids cancontrol the ion beam acceleration voltage within a range between 30 and200 V. The neutralizer 74 is provided outside the ion source 70 toneutralize ions.

The configuration of the ion source shown in FIG. 5 is similar to thatin an ion beam etching apparatus. However, according to the method ofthe present invention, the ion source is operated under conditionstotally different from those used for the ion beam etching apparatus, soas to carry out energy assisted oxidation under moderate, weakconditions. When the ion source is used as an etching apparatus, a highacceleration voltage of 200 to 500 V is applied to the positive grid 71to cause a reliable etching phenomenon. This hinders, for example, there-deposition of an etched material. In contrast, with the PIT and IAOprocesses according to the present invention, the ion beam is not usedto cause an etching phenomenon but for the following purposes. With PIT,the ion beam is used for an energy assistance effect for carrying outirradiation with energy to exert sucking action of the current pathmaterial from the underlayer. With IAO, the ion beam is used for anenergy assistance effect for oxidizing the material (Al or the like)forming an insulating layer that is easily oxidized, while carrying outa reduction reaction to form current paths (Cu or the like) that are noteasily oxidized. In either case, the ion beam is not used for theetching phenomenon but for the energy assistance effect. Thus, the PITand IAO processes according to the present invention normally use anacceleration voltage of about 30 to 130 V or at most 200 V for thepositive grid. Moreover, the actual preferable voltage range is between40 and 60 V. Such a voltage range is never used when the ion source isused as an etching apparatus. Moreover, the range of current valuesrepresenting the quantity of ion applied by the ion source is totallydifferent from that in the case of an etching apparatus. The etchingapparatus uses a current value of about 200 to 300 mA, while the PIT andIAO processes according to the present invention use a low current valueof 30 to 200 mA. Moreover, the actual preferable current value range isbetween 30 and 100 mA. The ion current, as used herein, is defined by acurrent I₊ flowing through the positive grid if the ion beam is used.However, a beam current I actually applied by the ion source iscalculated to be the difference between the absolute value of thecurrent I₊ flowing through the positive grid, and the absolute value ofa current I⁻ flowing through the negative grid, that is, I=(I₊)−(I⁻).The current flowing through the negative grid is normally set to as lowvalue as possible such as several mA.

The modifications described below may be made in order to stablygenerate plasma in such a low current range. For example, in the normalusage of an ion beam apparatus, the potential at the negative (V−) grid72 is set to a negative value so as to hinder electrons generated by theneutralizer 74 from flowing into the plasma in the ion source 70. In amodification, however, the potential at the negative (V⁻) grid 72 is setto a low potential value, that is, 0 or 10 V so that the neutralizer 74can be used not only to neutralize ions but also as an electron emissionsource for allowing electrons to flow into the plasma in the ion source70. Such a V− value enables electrons to flow into the ion source, whichcan then stably generate plasma even at a low current. In this case, thecurrent I₊, which flows through the positive grid, is actually the sumof a plasma current I_(+intrinsic) from the ion source and a currentI_(neut) resulting from electrons flowing from the neutralizer into thepositive grid. That is, when the negative grid is set for a negativevoltage with an absolute value of at least 10 V or more,I₊=I_(+intrinsic). In contrast, when the voltage at the negative grid isnot set to a minus value, I_(+intrinsic)=I₊−I_(neut). Consequently, theplasma current calculated by (I_(+intrinsic))−(I⁻) is the currentactually applied to the surface of a sample. This is equivalent todecrease in the effective current. That is, the current actually appliedto the sample can be significantly reduced below the apparent currentI₊, which flows through the positive grid in the apparatus. Thistechnique may be improved so that in addition to an electron source 74provided outside the ion source as shown in FIG. 5, another electronsource may be provided inside the ion source 70. The use of such amethod as required enables the substrate to be irradiated with a stableion beam with a low power and a low current during the PIT and IATprocesses.

The means described below may be used to irradiate the substrate with astable ion beam with a low power and a low current. For example, the ionsource may be provided with a permanent magnet or an electromagnet. Theion source may be an RF plasma source with a frequency of 13.56 MHz. Thelength of an oxygen conduit connecting the mass flow controller 63 forcontrolling the oxygen flow rate and the oxidation chamber 60 ispreferably within a range between 0 and 50 cm. A variable voltagemechanism may be provided which can maintain a fixed voltage of 10 to 50V during application of an ion beam. If the effect of allowing I_(neut)to flow into the ion source is used to stably generate plasma in a lowcurrent region, the mechanism can preferably control the voltage of theneutralizer to a fixed value so as to maintain a stable current value.

The above voltages and currents are also applicable to RF plasma. For RFplasma, the voltage is not the acceleration voltage for the grid but theplasma voltage automatically determined in connection with the RF powerdetermined. Further, the above numerical values correspond to preferableranges when wafer size is assumed to be six inches. However, with adifferent substrate size, the preferable range of the current value,which indicates the ion amount, corresponds to a value proportional tothe area of the wafer. The voltage value indicates the amount of energyand is thus corresponds exactly to the above preferable range regardlessof the wafer size.

Further, it is possible to control the depth from the film surface whichis affected by the ion beam treatment by varying the angle at which theion beam is incident on the substrate 1. If the ion beam isperpendicular to the film surface upon incidence, the effect of the ionbeam treatment covers a relatively large depth from the film surface. Ifthe ion beam is inclined at a small angle to the film surface, theeffect of the ion beam can be exerted only on the front side. However,the depth affected by the ion beam treatment also varies depending onthe time for the ion beam treatment. In the thickness direction, the ionbeam treatment can exert an equivalent effect with a short-time processwith a perpendicular incidence and with a long-time process with asmall-angle incidence. These treatment methods can be used depending onwhether or not to enhance an effect of two-dimensional migration ofatoms in the film surface.

In FIG. 4, an oxygen gas is introduced into the oxidation chamber 60.However, the oxygen gas may be introduced into the ion source 70 so asto carry out irradiation with an ion beam of the oxygen gas. In thiscase, since oxygen is applied as an ion beam, oxidation is activatedmore appropriately than when a simple oxygen gas flow is used. Thus, theoxidation ion beam conditions must further be weakened. Specifically,the conditions may be adjusted by reducing the acceleration voltage byabout 10 V, the treatment time by 10 seconds or more, or the incidentangle by 10° or more.

In the above description, the PIT and IAO processed are performed in theoxidation chamber 60 using an ion beam. However, the PIT and IAOprocesses may be performed in an RF plasma chamber in which RF plasma,which enables a similar treatment, can be generated. In this case, thePIT process may be performed in the metal deposition chamber. However,the IAO process is performed in an RF plasma chamber other than themetal deposition chamber. Taking the continuity of the processes intoconsideration, it is preferable that both the PIT and IAO processes besequentially performed in an RF plasma chamber other than the metaldeposition chamber. This is desirable also in order to keep the metaldeposition chamber clean. The preferable PIT/IAO conditions for the RFplasma are similar to that for the ion beam. That is, for the PITprocess, preferably the acceleration voltage is about 30 to 130 V, theplasma current, which replaces the beam current, is about 30 to 200 mA,and the RF power is about 10 to 300 W. For the IAO process, preferablythe acceleration voltage is about 30 to 200 V, the beam current is 30 to200 mA, and the RF power is about 10 to 300 W. However, with the RFplasma, setting the value of the RF power determines both accelerationvoltage and plasma current. This prevents these parameters from beingindependently controlled. Consequently, the controllability for the PITand IAO processes is inferior to that achieved when the ion beam isused. Further, also for the acceleration voltage, the use of the ionbeam enables acceleration to be achieved with a particular voltagevalue. However, with the RF plasma, the voltage range exhibitsdistribution varying over 10 V, resulting in degraded controllability.From this point of view, the ion beam is more preferably used than theRF plasma. In some cases, however, an RF plasma chamber may be morepreferable than an ion beam chamber in view of maintenance of equipment.Therefore, the ion beam or the RF plasma is selectively used accordingto need.

EXAMPLES

Examples of the present invention will be described below with referenceto the drawings. In the examples below, % representing the compositionsof alloys means atomic %.

Example 1

FIG. 6 is a perspective view of a magnetoresistive element (CCP-CPPelement) manufactured in the present example. The magnetoresistiveelement shown in FIG. 6 has a structure in which the films listed beloware sequentially stacked on a substrate (not shown):

lower electrode 11,

underlayer 12: Ta [5 nm]/Ru [2 nm],

pinning layer 13: Pt₅₀Mn₅₀ [15 nm],

pinned layer 14: Co₉₀Fe₁₀ [3.6 nm]/Ru [0.9 nm]/(Fe₅₀Co₅₀ [1 nm]/Cu [0.25nm])×2/Fe₅₀Co₅₀ [1 nm],

metal layer 15: Cu [0.5 nm],

spacer layer (CCP-NOL) 16: Al₂O₃ insulating layer 22 and Cu currentpaths 21 (prepared by depositing Al₉₀Cu₁₀ [1 nm], followed by performingPIT and IAO treatment),

metal layer 17: Cu [0.25 nm],

free layer 18: Co₉₀Fe₁₀ [1 nm]/Ni₈₃Fe₁₇ [3.5 nm],

cap layer 19: Cu [1 nm]/Ru [10 nm], and

upper electrode 20.

In the description below, the spacer 16 and the metal layers 15 and 17,disposed over and under the spacer layer 16, may be collectively calleda spacer layer. The CCP-CPP element shown in FIG. 6 is of a bottom typein which the pinned layer 14 is placed in the lower part. However, ofcourse, the CCP-CPP element may be of a top type in which the pinnedlayer 14 is placed in the upper part. A method for manufacturing theCCP-CPP element shown in FIG. 6 will be described in detail.

A lower electrode 11 is formed on the substrate (not shown); the lowerelectrode is used to supply a current perpendicularly to the spin valvefilm. Ta [5 nm] and Ru [2 nm] are deposited on the lower electrode 11 asan underlayer 12. Ta is a buffer layer that, for example, suppressesroughness of the lower electrode. Ru is a seed layer to control thecrystal orientation and the grain size of the spin valve film to bedeposited thereon.

The buffer layer may be made of Ta, Ti, W, Zr, Hf, Cr, or an alloythereof. The thickness of the buffer layer is preferably about 2 to 10nm, and more preferably 3 to 5 nm. The excessively small thickness ofthe buffer layer eliminates the buffer effect. The excessively largethickness of the buffer layer is not preferable because it increasesseries resistance, which does not contribute to the MR ratio. However,if the seed layer, deposited on the buffer layer, produces a buffereffect, the buffer layer consisting of Ta or the like need notnecessarily be provided.

The seed layer has only to be made of a material that can control thecrystal orientation of a layer formed thereon. The seed layer ispreferably a metal layer of an hcp or fcc structure. The use of Ru as aseed layer makes it possible to set the crystal of the spin-valve filmthereon to fcc (111) orientation and to appropriately keep the crystalorientation of PtMn to an ordered fct structure, and the crystalorientation of bcc metal to bcc (100) orientation. Further, the seedlayer enables the crystal grain size of the spin-valve film to becontrolled to 10 to 40 nm and makes it possible to achieve a high MRratio without varying characteristics even when the size of the CCP-CPPelement is reduced. A good crystal orientation can be realized;measurements based on X-ray diffraction indicate that rocking curves ofthe fcc (111) peak of the spin-valve film, the fct (111) peak of PtMnand the bcc (110) peak have a full width at half maximum of 3.5 to 6°.The dispersion angle of the orientation can also be determined fromdiffraction spots with a cross-sectional TEM.

The seed layer may be formed of, for example, Ni_(x)Fe_(100-x) (x=90 to50% and preferably 55 to 85%) or (Ni_(x)Fe_(100-x))_(100-y)X_(y) (X=Cr,V, Nb, Hf, Zr, Mo) which is made nonmagnetic by adding a third elementto NiFe instead of Ru. In the case where a NiFe-based seed layer isused, the crystal orientation is improved such that rocking curvesmeasured as described above have a full width at half maximum of 3 to5°. To obtain an appropriate crystal grain size of 10 to 40 nm,described above, the composition y of the third element X is preferablyin a range of about 0 to 30%. To increase the crystal grains above 40nm, a much larger amount of additive element can be used. For example,in the case of NiFeCr, it is preferable to add about 35 to 45% of Cr andto use a composition exhibiting the boundary phase between fcc and bcc.However, if the element is used as a read head adapted for high densityrecording, the element size will be 100 nm or less. Accordingly, anexcessively large crystal grain size may bring dispersion incharacteristics. Thus, it is not so preferable to use such an underlayermaterial that possibly forms grains larger than 40 nm. On the otherhand, if the element is used as, for example, MRAM, even an element witha size of 100 nm or more can be practically used in some applications.Accordingly, it is possible to use a seed layer that increases the grainsize in some cases.

The thickness of the seed layer is preferably about 1.5 to 6 nm, andmore preferably 2 to 4 nm. The excessively small thickness of the seedlayer eliminates effects such as crystal orientation control. Theexcessively large thickness of the seed layer increases a seriesresistance and may make the interface with the spin-valve filmirregular.

A pinning layer 13 is deposited on the underlayer 12. The pinning layer13 has a function for imparting unidirectional anisotropy to aferromagnetic layer constituting the pinned layer 14 deposited thereonto pin the magnetization of the pinned layer 14. Materials for thepinning layer 13 include antiferromagnetic materials such as PtMn,PdPTMn, IrMn, and RuRhMn. The thickness of the pinning layer 13 isappropriately set in order to apply unidirectional anisotropy of asufficient intensity. For PtMn or PdPtMn, the thickness is preferablyabout 8 to 20 nm, and more preferably 10 to 15 nm. IrMn or RuRhMn canimpart unidirectional anisotropy even with a thickness smaller than thatof PtMn or the like. Accordingly, for IrMn or RuRhMn, the thickness ispreferably 5 to 18 nm, and more preferably 7 to 15 nm. Since IrMn canimpart one-directional anisotropy even if the thickness thereof issmaller than that of PtMn, IrMn is suitable to address the narrow gaprequirement for high-density recording. Therefore, IrMn isadvantageously used for a head adapted to high-density recording. A hardmagnetic layer may be used in place of these antiferromagnetic layers.Hard magnetic layers include, for example, CoPt (Co=50 to 85%),(Co_(x)Pt_(100-x))_(100-y)Cr_(y) (x=50 to 85%, y=0 to 40%), FePt (Pt 40to 60%). Because of its low specific resistance, the hard magneticlayer, in particular CoPt, serves to suppress adverse effects such asincreases in series resistance and RA.

A pinned layer 14 is formed on the pinning layer 13. The pinned layer 14in the present Example is a synthetic pinned layer of a lower pinnedlayer 14 a (Co₉₀Fe₁₀), an Ru layer 14 b, and an upper pinned layer 14 c(Fe₅₀Co₅₀ [1 nm]/Cu [2.5 nm]×2/Fe₅₀Co₅₀ [1 nm]). The pinning layer(PtMn) 13 and the lower pinned layer 14 a, located immediately above thepinning layer 13, are exchange-coupled so as to have unidirectionalanisotropy. The lower pinned layer 14 a and upper pinned layer 14 c,arranged under and over the Ru layer 14 b, respectively, are stronglymagnetically coupled so as to have antiparallel magnetizationdirections.

The lower pinned layer 14 a is preferably designed to have a magneticthickness, that is, saturation magnetization Bs×thickness t (Bs*tproduct), almost equal to that of the upper pinned layer 14 c. In thepresent Example, the upper pinned layer 14 c is (Fe₅₀Co₅₀ [1 nm]/Cu [2.5nm])×2/Fe₅₀Co₅₀ [1 nm] and FeCo has a saturation magnetization of about2.2 T. Consequently, the magnetic thickness is 2.2 T×3 nm=6.6 Tnm. Forthe lower pinned layer 14 a, since Co₉₀Fe₁₀ has a saturationmagnetization of about 1.8 T, the thickness t of the lower pinned layer14 a required to provide a magnetic thickness equal to that describedabove is 6.6 Tnm/1.8 T=3.66 nm. The present Example uses Co₉₀Fe₁₀ ofthickness 3.6 nm. In connection with the unidirectional anisotropicfield intensity of the pinning layer (PtMn) and the antiferromagneticcoupling field intensity between lower pinned layer and upper pinnedlayer, located under and over Ru, respectively, the magnetic layer usedas a lower pinned layer preferably has a thickness of about 2 to 5 nm.In view of the coupling field, when the lower pinned layer has anexcessively small thickness, the upper pinned layer will also be used ina small thickness. Since the upper pinned layer greatly contributes tothe MR effect, to make the upper pinned layer thin implies that the MRratio is reduced. As a consequence, to use a lower pinned layer with anexcessively small thickness brings about reduction of the MR ratio.Inversely, an excessively large thickness compared to the above rangemakes it difficult to obtain a sufficient unidirectional anisotropicfield required for device operation.

The lower pinned layer 14 a may be made of, for example, aCo_(x)Fe_(100-x) alloy (x=0 to 100%), a Ni_(x)Fe_(100-x) alloy (x=0 to100%), or either of these alloys with a nonmagnetic additive element.The lower pinned layer 14 a may be made of an elementary substance ofCo, Fe or Ni, or an alloy thereof.

The Ru layer 14 b has a function for producing antiferromagneticcoupling between the magnetic layers located over and under the Ru layer14 b to form a synthetic pinned structure. The Ru layer 14 b preferablyhas a thickness of 0.8 to 1 nm. A material other than Ru may be usedprovided that it produces sufficient antiferromagnetic coupling betweenthe magnetic layers located over and under thereof.

The upper pinned layer 14 c (Fe₅₀Co₅₀ [1 nm]/Cu [2.5 nm]×2/Fe₅₀Co₅₀ [1nm]) constitutes a part of a spin-dependent scattering unit. That is,the upper pinned layer 14 c is a magnetic layer that directlycontributes to the MR effect. Therefore, both the film materials and thedesign in thicknesses of the upper pinned layer 14 c are very importantin order to obtain a large MR ratio. In particular, the magneticmaterial located at the interface with the spacer layer is important interms of contribution to spin-dependent interface scattering. Thepresent Example uses Fe₅₀Co₅₀ with a bcc structure.

If a magnetic material having the bcc structure is used for theinterface with the spacer layer, its high spin-dependent interfacescattering effect enables a high MR ratio to be achieved. FeCo-basedalloys having the bcc structure include Fe_(x)Co_(100-x) (x=30 to 100%)and Fe_(x)Co_(100-x) to which an additive element is added. The metalmaterial used for the spin-valve film often has the fcc or fctstructure, so that only the upper pinned layer may have the bccstructure. Thus, the excessively small thickness of the upper pinnedstructure is not preferable because it prevents the bcc structure frombeing kept stable, which precludes a high MR ratio from being achieved.The magnetic material functions as an upper pinned layer (pinned layerbetween the spacer layer and the Ru layer) preferably has a thickness of2 nm or more; the thickness is preferably 5 nm or less in order toobtain a large pinning field. Further, if the pinned layer is formed ofa magnetic layer having the bcc structure, which is likely to achieve ahigh MR ratio, the layer having the bcc structure preferably has a totalthickness of 2 nm or more in order to maintain the bcc structure morestable. The range of thickness of the pinned layer having the bccstructure is preferably set between 2.5 and 4 nm in order to maintaincompatibility of the pinning field and the stability of the bccstructure. Also, a material having the composition range from Fe₇₅Co₂₅to Fe₈₅Co₁₅, which brings about more stable bcc structure, can be used.The upper pinned layer may be made of a CoFe alloy having the fccstructure or a cobalt alloy having the hcp structure, in place of themagnetic material having the bcc structure. It is possible to use any ofelementary metals such as Co, Fe, and Ni and alloys containing any oneof these metals. The most advantageous upper pinned layer material forgaining a high MR ratio is a FeCo alloy material having the bccstructure. The second and third most advantageous upper pinned layermaterials are a cobalt alloy having a cobalt composition of 50% or moreand a nickel alloy having a nickel composition of 50% or more.

In the present Example, the upper pinned layer is composed of a magneticlayer (FeCo layer) and a nonmagnetic layer (very thin Cu layer)alternately stacked. The upper pinned layer having such a structure alsomakes it possible to improve a spin-dependent scattering effect, calleda bulk scattering effect. In the CCP-CPP element, current is confinednear the spacer to greatly enhance the contribution of the resistancenear the interface with the spacer layer. In this case, the interfacescattering effect makes greater contribution than the bulk scatteringeffect. Accordingly, in the CCP-CPP element, selection of the materiallocated at the interface of the spacer layer and the upper pinned layeris significantly important compared to a conventional CPP element.Nevertheless, it is also effective to use a material producing asignificant bulk scattering effect in order to obtain a higher MR ratio.The thickness of the thin Cu layer, which enhances the bulk scatteringeffect, between the magnetic layers is preferably between 0.1 and 1 nm,and more preferably between 0.2 and 0.5 nm. The excessively smallthickness of the Cu layer weakens the effect of improving the bulkscattering effect. The excessively large thickness of the Cu layer isnot preferable because it may degrade the bulk scattering effect andweakens the magnetic coupling between the magnetic layers located overand under the nonmagnetic CU layer to make the characteristics of thepinned layer insufficient. The nonmagnetic material between the magneticlayers may be Hf, Zr, Ti, or the like, in place of Cu. On the otherhand, the thickness per single layer of the magnetic layer such as FeCo,in the case where a thin nonmagnetic layer is inserted therebetween, ispreferably between 0.5 and 2 nm and more preferably between 1 and 1.5nm.

The upper pinned layer may be made of an alloy of FeCo and Cu instead ofa stack of a FeCo layer and a Cu layer. Such a FeCoCu alloy is, forexample, (Fe_(x)Co_(100-x))_(100-y)Cu_(y) (x=about 30 to 100%, y=about 3to 15%). However, a different compositional range may be used. Theelement added to FeCo may be Hf, Zr, Ti, or the like in place of Cu. Theupper pinned layer may be a single-layer film of Co, Fe, Ni, or an alloythereof. For example, as the simplest structure, a single layer ofCo₉₀Fe₁₀ may be used for an upper pinned layer. An additive element maybe added to such a material.

As described above with reference to FIG. 2A, a Cu film is deposited onthe pinned layer 14 as a first metal layer serving as a source of thecurrent paths 21 in the spacer layer 16. Then, an AlCu layer isdeposited as a second metal layer to be converted into the insulatinglayer 22 in the spacer layer 16. As described above with reference toFIG. 2B, a pretreatment (PIT) for oxidation is performed by irradiatingthe AlCu layer, the second metal layer, with an ion beam of a rare gas.In this process, Ar ions are applied at an acceleration voltage of 30 to130 V, a beam current of 20 to 200 mA, and a treatment time of 30 to 180seconds. In the present Example, within the above acceleration voltagerange, particularly a voltage of 40 to 60 V is used. This is because ahigher voltage range may lower the MR ratio owing to, for example, thesurface roughened by PIT in some cases. Further, the current value usedis between 30 and 80 mA, and the irradiation time used is between 60 and150 seconds. The deposited first metal layer (Cu layer) is present inthe form of a two-dimensional film. The PIT process causes Cu of thefirst metal layer to be sucked up in the AlCu layer by which Cu intrudesinto the AlCu layer. The Cu intruding the AlCu layer remains in a metalstate as is after the later oxidation process is performed and forms thecurrent paths. Thus, it is important to perform an energy treatment suchas the PIT after the deposition of the second metal layer. Then, asdescribed above with reference to FIG. 2C, the AlCu layer, the secondmetal layer, is subjected to ion beam-assisted oxidation (IAO). In thisprocess, Ar ions are applied at an acceleration voltage of 40 to 200 V,a beam current of 30 to 200 mA, and a treatment time of 15 to 300seconds, with oxygen supplied. In the present Example, within the aboveacceleration voltage range, a voltage of 50 to 100 V is particularlyused. This is because a higher voltage range may lower the MR ratioowing to, for example, the surface roughened by PIT in some cases.Further, the current value used was between 40 and 100 mA, and theirradiation time used was between 30 and 180 seconds. Since Al is easilyoxidized but Cu is not, a spacer 16 is formed which has an insulatinglayer 22 of Al₂O₃ and current paths 21 of Cu. In the present Example,the range of the oxygen exposure amount during the oxidation by IAO ispreferably between 2,000 and 4,000 L. It is not preferable to oxidizenot only Al but also the lower magnetic layer during IAO. This isbecause the oxidation may degrade the heat resistance and reliability ofthe CCP-CPP element. To improve reliability, it is important that themagnetic material located under the CCP spacer layer is not oxidized butis present in a metal state. To achieve this, the amount of oxygen mustbe controlled within the above range of the oxygen exposure amount. Toform a stable oxide by supplied oxygen, oxygen gas is desirably providedonly during the irradiation of the substrate surface with an ion beam.Desirably, no oxygen gas is provided while the substrate surface is notirradiated with an ion beam.

The thickness of the Cu layer is adjusted depending on the thickness ofthe AlCu layer. The greater thickness of the AlCu layer requires anincrease in the amount of Cu intruding the AlCu layer during the PITprocess. Accordingly, the thickness of the Cu layer must be increased.For example, when AlCu has a thickness of 0.6 to 0.8 nm, the Cu layerhas a thickness of about 0.1 to 0.5 nm. When AlCu has a thickness of 0.8to 1 nm, the Cu layer has a thickness of about 0.3 to 1 nm. Theexcessively small thickness of the Cu layer prevents a sufficient amountof Cu from being supplied to the AlCu layer during the PIT process. Thisprecludes the Cu current paths from penetrating the AlCu layer to theupper end thereof. In this case, the area resistance RA is too high andthe MR ratio has an insufficient value. On the other hand, excessivethickness of the Cu layer allows a sufficient amount of Cu to besupplied to the AlCu layer during the PIT process but finally leaves athick Cu layer between the pinned layer 14 and the spacer layer 16. Toachieve a high MR ratio in the CCP-CPP element, a current confined inthe spacer layer 16 must reach the magnetic layer while keeping theconfined state. However, it is not preferable that a thick Cu layerremain between the pinned layer 14 and the spacer layer 16. This isbecause the current confined in the spacer layer 16 is extended beforereaching the magnetic layer, thus lowering the MR ratio.

Instead of Cu, Au, Ag, or the like may be used as a material for thefirst metal layer, which forms current paths. However, Cu is preferablebecause it is more stable against a heat treatment than Au and Ag. Inplace of these nonmagnetic materials, a magnetic material may be usedfor the first metal layer. Magnetic materials include Co, Fe, Ni, and analloy thereof. If the same magnetic material is used for the pinnedlayer and for the current paths, the source (first metal layer) of thecurrent paths need not be provided on the pinned layer. That is, byforming, on the pinned layer, a second metal layer to be converted intothe insulating layer and then performing the PIT process, it is possibleto allow the material for the pinned layer to intrude into the secondmetal layer to form current paths of the magnetic material.

If Al₉₀Cu₁₀ is used as a second metal layer, not only Cu of the firstmetal layer is sucked up but also Cu in AlCu is separated from Al toform current paths during the PIT process. Furthermore, if ionbeam-assisted oxidation is carried out after the PIT process, theoxidation proceeds with the ion beam assistance effect facilitating theseparation of Cu from Al. Instead Al₉₀Cu₁₀, a single metal of Al notcontaining Cu, a current path material, may be used for the second metallayer. In this case, Cu, the current path material, is supplied onlyfrom the first metal layer, located under the second metal layer. IfAlCu is used for the second metal layer, Cu, the current path material,is also supplied from the second metal layer during the PIT process.Thus, advantageously, current paths can be relatively easily formed evenif a thick insulating layer is to be formed. If Al is used for thesecond metal layer, Cu cannot mix easily into Al₂O₃ formed by oxidation.Thus, advantageously, Al₂O₃ with a high voltage resistance is easilyformed. Each of the cases of using Al and using AlCu exhibits aparticular advantage. Therefore, the material of the second metal layermay be selected according to conditions.

The thickness of the second metal layer is about 0.6 to 2 nm for AlCuand about 0.5 to 1.7 nm for Al. The thickness of the insulating layerformed by oxidizing the second metal layer is about 0.8 to 3.5 nm. Aninsulating layer can be easily produced which has a thickness of about1.3 to 2.5 nm after oxidation; such an insulating layer is alsoadvantageous in current confined effect. Further, the current pathspenetrating the insulating layer have a size of about 1 to 10 nm, morepreferably 2 to 6 nm. Metal paths with a size larger than 10 nm are notpreferable because they bring about dispersion of device characteristicswhen the device size is reduced. It is preferable that metal paths witha size larger than 6 nm are not present in the device.

AlCu as a second metal layer preferably has a composition represented byAl_(x)Cu_(100-x) (x=100 to 70%). An additive element such as Ti, Hf, Zr,Nb, Mg, Mo, or Si may be added to AlCu. In this case, the composition ofthe additive element is preferably about 2 to 30%. The addition of suchan additive element may facilitate the formation of a CCP structure.Further, when a larger amount of such an additive element is distributedin the boundary area between the Al₂O₃ insulating layer and the Cucurrent paths than in the other areas, adhesion between the insulatinglayer and the current paths is improved, which brings about an effect ofimproving electromigration resistance in some cases. In the CCP-CPPelement, a very high current density of 10⁷ to 10¹⁰ A/cm² is achieved inthe metal current paths in the spacer layer. Accordingly, it isimportant to improve the electromigration resistance and to keep the Cucurrent paths stable during current supply. However, with an appropriateCCP structure formed, a sufficiently high electromigration resistancecan be provided without adding any additive element to the second metallayer.

The material for the second metal layer is not limited to the Al alloy,which forms Al₂O₃, but may be an ally mainly composed of Hf, Mg, Zr, Ti,Ta, Mo, W, Nb, Si, or the like. Further, the insulating layer into whichthe second metal layer is converted is not limited to the oxide but maybe a nitride or an oxynitride. Whatever material is used for the secondmetal layer, the second metal layer preferably has a thickness of about0.5 to 2 nm after deposition and a thickness of about 0.8 to 3.5 nmafter conversion into an oxide, a nitride, or an oxynitride.

Cu [0.25 nm] is deposited on the spacer layer 16 as a metal layer 17.The metal layer 17 functions as a barrier layer that prevents the freelayer deposited thereon from contacting the oxide in the spacer layer16. The insulating layer in the spacer layer may be an amorphous layer.In this case, use of Cu exhibiting a stable fcc structure as the metallayer 17 is preferable because this brings about an effect of improvingcrystallinity deposited thereon. However, since these problems may beavoided by optimization of anneal conditions, selection of an insulatingmaterial in the spacer layer, and a material of free layer, the metallayer 17 on the spacer layer 16 need not necessarily be provided. Thus,the metal layer 15, located under the spacer layer 16, is essentialbecause it is a source of current paths. On the other hand, the metallayer 17 on the spacer layer 16 is not essential. However, in view ofthe purposes to ensure a process margin or stability in characteristics,it is practically preferable to form the metal layer 17 of Cu on thespacer layer 16. Instead of Cu, Au, Ag, Ru, or the like may be used as amaterial for the metal layer 17. However, the material for the metallayer 17 is preferably the same as that for the current paths in thespacer layer 16. If different materials are used for the metal layer 17and for the current paths, the interface resistance increases. However,this is prevented if the same material is used for both components. Thethickness of the metal layer 17 is preferably between 0 and 1 nm, andmore preferably between 0.1 and 0.5 nm. The excessively large thicknessof the metal layer 17 extends a current confined by the spacer layer 16to make the current confined effect insufficient, resulting in loweringof the MR ratio. The effect provided by the use of the metal layer 17and the disadvantage that the current confined effect becomesinsufficient due to excessively thick metal layer 17 are balanced in theabove thickness range, which is the reason why the above thickness ispreferred.

Co₉₀Fe₁₀ [1 nm] and Ni₈₃Fe₁₇ [3.5 nm] are deposited on the metal layer17 as a free layer 18. Selection of the magnetic material for the freelayer 18 located at the interface with the spacer layer is important forachieving a high MR ratio. In this case, a CoFe alloy is more preferablyprovided at the interface with the spacer layer than a NiFe alloy. Ofthe CoFe alloys, Co₉₀Fe₁₀, which has a particularly stablesoft-magnetism, is used in the present Example. If a CoFe alloy nearCo₉₀Fe₁₀ is used, it preferably has a thickness of 0.5 to 4 nm. If aCoFe alloy of a different composition (for example, the compositiondescribed in connection with the pinned layer) is used, it preferablyhas a thickness of 0.5 to 2 nm. If the free layer is composed of, forexample, Fe₅₀Co₅₀ (or Fe_(x)Co_(100-x) (x=45 to 85)) similarly to thepinned layer in order to enhance the spin-dependent interface scatteringeffect, an excessively large thickness must be avoided in order tomaintain the soft-magnetism of the free layer. Consequently, thepreferable thickness range is between 0.5 and 1 nm. If Fe free from Cois used, the thickness may be between about 0.5 and 4 nm because thismetal has a relatively good soft-magnetism. The NiFe layer provided onthe CoFe layer is a material having the most stable soft-magnetism. TheCoFe alloy does not have a very stable soft magnetism but its softmagnetism can be supplemented by providing the NiFe alloy thereon. Sincea material capable of achieving a high MR ration can be used at theinterface to the spacer layer, it is preferable to use NiFe as the freelayer to improve characteristics of the spin-valve as a whole. Thecomposition of the NiFe alloy is preferably Ni_(x)Fe_(100-x) (x=about 78to 85%). The present Example uses the composition (Ni₈₃Fe₁₇) containinga larger amount of Ni than the composition Ni₈₁Fe₁₉ of common NiFe. Thisis because if a free layer is formed on a spacer layer having the CCPstructure, the Ni composition for realizing zero magnetostrictiondeviates slightly from the common NiFe. Specifically, magnetostrictionof the CoFe shifts toward positive when it is deposited on the spacerlayer of CPP structure compared to the case that it is deposited on ametal Cu spacer layer. Thus, it is preferable to use NiFe containingmore Ni than common NiFe, which makes it possible to shift themagnetostriction toward negative, to cancel the above magnetostrictionshift toward positive. The NiFe layer preferably has a thickness ofabout 2 to 5 nm. If the NiFe layer is not used, a free layer may be usedin which a plurality of CoFe or Fe layers with a thickness of about 1 to2 nm and a plurality of very thin Cu layers with a thickness of about0.1 to 0.8 nm are alternately stacked.

Cu [1 nm] and Ru [10 nm] are stacked on the free layer 18 as a cap layer19. The cap layer 19 has a function for protecting the spin-valve film.The Cu layer preferably has a thickness of about 0.5 to 10 nm. An Rulayer may be provided directly on the free layer 18 to a thickness ofabout 0.5 to 10 nm without providing any Cu layer. When NiFe is used inthe free layer on the side of the cap layer, opposite to the spacerside, magnetostriction of an interface mixing layer formed between thefree layer and the cap layer can be lowered because of non-solublerelationship between Ru and Ni, which brings about preferred effect. Inplace of the Cu or Ru layer, another metal layer may be used. Theconfiguration of the cap layer is not particularly limited and anymaterial may be used provided that it can produce a capping effect. Itshould be noted that, however, the material selected for the cap layermay affect the MR ratio and long-term reliability. Cu and Ru aredesirable material for the cap layer in view of these characteristics.An upper electrode 20 is formed on the cap layer 19 to supply a currentperpendicularly to the spin-valve film.

The CCP-CPP element of the present Example indicated characteristics ofRA=500 mΩμm², MR ratio=9%, and ΔRA=45 mΩμm². Such a high MR ratio wasachieved because the selection of the appropriate PIT and IAO ion beamconditions as described above enabled the improvement of purity of theCu current paths. Such a CCP-CPP element makes it possible to provide aread head that can be adapted to a recording density of 150 to 300 Gpsi.Further, when the above PIT and IAO ion beam parameters had largervalues, RA changed to a smaller value. The following values wereobtained: RA=300 mΩμm², MR ratio=8.5%, and ΔRA=25.5 mΩμm². By settingstronger conditions for the PIT and IAO ion beam parameters, it ispossible to increase the density of current paths of the CCP structurein the film two-dimensional surface to reduce the resistance RA.

The larger values for the ion beam parameters mean an increased beamenergy value, an increased beam current value, an extended beamirradiation time, and the like.

The bottom type CCP-CPP element has been described in which the pinnedlayer is located below the free layer. However, the method according tothe embodiment of the present invention is similarly applicable to a toptype CCP-CPP element. To manufacture a top type CCP-CPP element, thelayers provided between the underlayer 12 and the cap layer 19 in FIG. 6may be deposited in the order opposite to that shown in FIG. 6. Thefunctions of the metal layers (Cu layers) located over and under thespacer layer provide the same functions for both top- and bottom-typeCCP-CPP elements. That is, the Cu layer under the spacer layer isessential because it is a source of current paths. However, the Cu layerover the spacer layer is not essential.

Example 2

Comparison between the characteristics of CCP-CPP elements produced byvarious methods will be described. The materials for the layers from theunderlayer 12 to the cap layer 19 are listed below:

underlayer 12: Ta [5 nm]/Ru [2 nm],

pinning layer 13: Pt₅₀Mn₅₀ [15 nm],

pinned layer 14: Co₉₀Fe₁₀ [4 nm]/Ru [0.9 nm]/Co₉₀Fe₁₀ [4 nm],

metal layer 15: Cu [2.5 nm],

spacer layer (CCP-NOL) 16: Al₂O₃ insulating layer and Cu current paths21 (prepared by depositing Al₉₀Cu₁₀ [x nm], followed by performing PITand IAO treatment),

metal layer 17: Cu [2.5 nm],

free layer 18: Co₉₀Fe₁₀ [1 nm]/Ni₈₃Fe₁₇ [3.5 nm],

cap layer 19: Cu [1 nm]/Ru [10 nm].

In the present example, the thickness x of AlCu, used as a second metallayer, was varied between 0.5 and 1 nm. To vary the thickness of AlCucorresponds to vary the area ratio of the current paths in the CCP-NOLsurface, and thus, this enables to adjust RA of the CCP-CPP element.That is, RA increases consistently with the thickness of AlCu. In thepresent example, Co₉₀Fe₁₀ was used as a magnetic material for bothpinned and free layers located adjacent to the spacer layer. In the casewhere Co₉₀Fe₁₀ is used, the MR ratio is reduced compared to the case ofFe₅₀Co₅₀/Cu used in Example 1. However, the present example uses thesimple structure in order to compare manufacturing methods with oneanother.

In this Example 2, a method of forming a first and second metal layersand then forming CCP-NOL using the PIT and IAO processes. To comparewith the above method, the methods described below were used.

Comparative Example 1

Method of Forming a First and Second Metal Layers and Then FormingCCP-NOL Using Natural Oxidation (NO) Without the PIT Process.

Comparative Example 2

Method of Forming a First and Second Metal Layers and Then FormingCCP-NOL Using the IAO Process Without the PIT Process.

FIG. 7 shows the relationship between the RA and MR ratio of CCP-CPPelements manufactured by using the above methods.

For reference, the characteristics of a metal CPP element using Cu [5nm] as a spacer layer were: RA=100 mΩμm², ΔRA=0.5 mΩμm², and MRratio=0.5%.

In the case of Comparative Example 1 where CCP-NOL was formed by naturaloxidation, the MR ratio increased consistently with RA and 1.5% at RA of380 mΩμm². Both RA and MR ratio were higher than those for the metal CPPelement. This indicates that the presence of CCP-NOL improves the MRratio.

When a CCP-CPP spin-valve film structure can be implemented, the MRratio increases consistently with RA until RA reaches a range between500 and 1,000 mΩμm². However, in principle, a further increase in RAsaturates the MR ratio into an almost constant value. Actually, forelements exhibiting RA of 1,000 mΩμm² or more, not only the currentpaths have a reduced area ratio but also RA may be increased due tooxidation of the lower magnetic layer or other adverse affects. Thus,when RA becomes over 1,000 mΩμm², the MR ratio may decrease.

In the case of Comparative Example 2 where CCP-NOL was formed by the IAOprocess, the MR ratio was 2.5% at RA of 500 mΩμm². In contrast toComparative Example 1, the value of the MR ratio could be nearly doubledat the same RA.

In the case of Example 2 where CCP-NOL was formed by the PIT and IAOprocesses, the MR ratio was 5.5% at RA of 500 mΩμm². That is, thepresent Example achieved a high MR ratio at least twice as high as thatin Comparative Example 2 and at least four times as high as that inComparative Example 1.

FIG. 8 shows an R-H loop of the CCP-CPP element produced according toExample 2. The R-H loop was measured at a field intensity of H=600 Oe orless taking practical uses into account. It has been reported that iflocal pinholes function as current paths are created in a TMR elementwhen a very thin insulating layer is used, the R-H loop thereof isshifted to be asymmetric to the magnetic field due to influence of alocal current field (see B. Oliver et al., J. Appl. Phys., 91, 4348(2002)). However, as shown in FIG. 8, the R-H loop of the CCP-CPPelement produced according to the present example is symmetric to themagnetic field. This indicates that the method according to the presentinvention permits to form a satisfactory CCP-NOL in which a large numberof current paths are formed in the insulating layer uniformly.

The principle of improvement of the MR ratio by the formation of CCP-NOLusing the method according to the present invention will be discussedbelow. Here, the discussion will be based on the model proposed by Valetand Fert, referred to as a Valet-Fert model hereinafter (T. Valet and A.Fert, Phys. Rev. B 48, 7099 (1993)). To discuss experiments according tothe present example, the Valet-Fert model must be adapted to the CCP-CPPelement. The following assumption was made in order to extend theValet-Fert model. That is, in the CCP-CPP element, a current is confinedin the current paths in the spacer layer, so that the area of theinterface between the spacer layer and the pinned layer or free layer isdependent on the area ratio D [%] of the current paths. Further, in theCCP-CPP element, the resistance of the spacer layer accounts for alarger percentage of the total resistance. Consequently, of thespin-dependent scattering, the interface scattering effect is moresignificant than the bulk scattering effect. Thus, the bulk scatteringeffect is neglected for simplification of calculations herein.

FIG. 9A shows a perspective view of the CCP-CPP element according toExample 2. FIG. 9B shows an enlarged perspective view of a current path.FIG. 9C shows an equivalent circuit diagram of the CCP-CPP elementaccording to the present example.

In FIG. 9C, RA_(upper) denotes the area resistance of the cap layer 19and upper electrode, located above the free layer 18. RA_(free) denotesthe area resistance of the free layer 18. RA_(pinned) denotes the arearesistance of the upper pinned layer 14 c, sandwiched between Ru andCCP-NOL, which contributes to the GMR effect. RA_(lower) denotes thearea resistance of Ru 14 b, lower pinned layer 14 a, pinning layer 12,underlayer 12, and lower electrode, located above the upper pinned layer14 c. As shown in FIG. 9C, the resistance of the Cu current path inCCP-NOL is determined by diving the product of the specific resistanceρ_(Cu) and thickness t_(Cu) of the Cu current path by the area ratio Dof the current path, that is, ρ_(Cu)t_(Cu)/(D/100). The interfaceresistance between the current path and the free layer 18 or upperpinned layer 14 c (in both interfaces, the current path is in contactwith CoFe) is determined by dividing RA_(CoFe/Cu) by the area ratio D ofthe current path taking an interface scattering coefficient γ intoaccount, that is, RA_(CoFe/Cu)/(1−γ²)/(D/100).

In the above model, RA_(CCP) of CCP-NOL is expressed by equation (1),and ΔRA_(interface) is expressed by equation (2).

$\begin{matrix}{{RA}_{CCP} = {\frac{\left\{ {{2{{RA}_{{CoFe}/{Cu}}/\left( {1 - \gamma^{2}} \right)}} + {\rho_{Cu}t_{Cu}}} \right\}}{\left( {D/100} \right)}\mspace{14mu}\left\lbrack {m\;\Omega\;{\mu m}^{2}} \right\rbrack}} & (1) \\\begin{matrix}{{\Delta\;{RA}_{interface}} = \frac{\left( {{\Delta\;{RA}_{{pinned}/{spacer}}} + {\Delta\;{RA}_{{free}/{spacer}}}} \right)}{\left( {D/100} \right)}} \\{= {\frac{\left( {4\gamma\;{{RA}_{{CoFe}/{Cu}^{2}}^{*}/\left( {{\rho_{Cu}t_{Cu}} + {2{RA}_{{CoFe}/{Cu}}^{*}}} \right)}} \right)}{\left( {D/100} \right)}\mspace{14mu}\left\lbrack {m\;\Omega\;\mu\; m^{2}} \right\rbrack}}\end{matrix} & (2)\end{matrix}$

On the basis of these models, the relationship between the RA and MRratio of the CCP-CPP spin-valve film was calculated. First, the RA valueexcept for RA_(CCP) was set to 100 mΩμm². This value was introduced froman RA value experimentally determined for a metal CCP element.RA_(CoFe/Cu) was set to 0.2 mΩμm² on the basis of document values. Thethickness t_(Cu) was set to 1.5 nm, which was equal to the thickness ofCCP-NOL obtained from cross-sectional TEM observation. The interfacescattering coefficient γ was set to 0.62, which was experimentallydetermined for a metal CCP element. FIG. 7, already described, showslines obtained by fitting experimental data on the MR ratio to RA usingthe above values and using the specific resistance ρ_(Cu) of the Cucurrent path in CCP-NOL as a parameter.

As shown in FIG. 7, the experimental data appropriately match thefitting lines. This indicates that calculations based on the models forwhich the CCP-NOL structure is assumed are valid. For ComparativeExample 1 (natural oxidation) and Comparative Example 2 (IAO), thefitting lines express the tendency in which the MR ratio increasesconsistently with RA until RA reaches about 500 mΩμm² and in which afurther increase in RA almost saturates the MR ratio. Therefore, theimprovement of the MR ratio in FIG. 7 can be described as the effect ofthe CCP-NOL structure.

Further discussion will be made by focusing on the specific resistanceρ_(Cu) of the CU current path, the parameter used for the fitting inFIG. 7. The specific resistance ρ_(Cu) is 160 μΩcm in ComparativeExample 1 (natural oxidation), 110 μΩcm in Comparative Example 2 (IAO),and 65 μΩcm in Example 2 (PIT and IAO). The specific resistance ρ_(Cu)of the Cu current path in Comparative Example 2 is lower than that inComparative Example 1. This indicates that IAO increases the purity ofthe Cu current path beyond that achieved by natural oxidation. IfCPP-NOL is formed by natural oxidation, not only Al but also Cu areoxidized to some degree. In contrast, if IAO is used to form CPP-NOL, Althat is low in energy of oxidation is easily oxidized, but Cu that ishigh in energy of oxidation is not easily oxidized because of a reducingeffect accompanied by Ar ion beam assist.

When CPP-NOL is formed by PIT and IAO (Example 2), the purity of the Cucurrent path is higher than that achieved when CPP-NOL is formed only byIAO (Comparative Example 2). This is because the PIT process before IAOseparates Cu from Al and because the suction phenomenon from theunderlying Cu layer causes the formation of Cu paths. That is, theimportant factors determining the purity of the Cu current paths are (1)the degree of separation of the Cu paths from Al in the metal stateprior to oxidation (formation of Cu paths penetrating the Al layeracross the thickness) and (2) the oxidation only of Al and the avoidanceof oxidation of Cu during oxidation process. PIT can facilitate theseparation of Cu from Al before oxidation to realize the effect (1),thus allowing the effect (2) to be easily established. In addition,during the oxidation process, IAO is more preferable than naturaloxidation for allowing the effect (2) to be realized particularlyeasily. Moreover, natural oxidation without energy assistance is notsubstantially be expected to produce the effect (1) during oxidation.However, energy assisted IAO also enables to facilitate the separationphenomenon in (1) during oxidation (formation of Al₂O₃ and separation ofmetal Cu before oxidation), thus achieving a high MR ratio.

As described above, the PIT and IAO process improves the MR ratiobecause it reduces the specific resistance of the Cu current paths inthe CCP-NOL structure, in other words, the process increases the purityof Cu in the Cu current paths.

The PIT process according to the present invention is based on thesuction of Cu from the first metal layer. Typical experiment resultsregarding this phenomenon will be described below. When an AlCu alloy asa second metal layer is formed without forming a first metal layer (Culayer) in advance, the PIT and IAO process cannot realize a low RA andaccordingly a high MR ratio. That is, if the first metal layer (Culayer) is not formed, the Cu current paths cannot be formed even withthe PIT and IAO process. This indicates that Cu cannot perfectly beseparated from Al if the PIT process is applied to the AlCu alloy. Onthe other had, in the case where the first metal layer (Cu layer) isformed, even if a single metal Al free from Cu is used as a second metallayer, the PIT/IAO process gives a low RA and a high MR ratio. When Alas a second metal layer is formed without forming a first metal layer(Cu layer) in advance, the PIT and IAO process cannot significantlylower RA and gives a low MR ratio. These results indicate that as longas the first metal layer (Cu layer) is formed, current paths are formedeven if the second metal layer is made of Al not containing Cu.Therefore, with the PIT and IAO process according to the presentinvention, the PIT process causes the suction of Cu from the first metallayer, and IAO allows the formation of good current paths penetratingthe insulating layer. The suction of Cu from the underlying Cu layer byPIT has been confirmed by XPS surface analysis for a model sample, inwhich the phenomenon that the PIT process causes the underlying metal tobe sucked up so as to penetrate the Al layer is observed. Specifically,XPS surface analysis for the structure of underlayer/Cu [0.25 nm]/Al[0.9 nm]/cap indicates that Cu peaks are weak when PIT is not performedbut the PIT process causes significant increase of Cu peakscorresponding to increase in the concentration of Cu in the filmsurface.

FIGS. 10A and 10B show the I-V and R-V characteristics, respectively, ofa CCP-CPP element produced via the PIT/IAO process according to thepresent example. As shown in FIG. 10A, the CCP-CPP element exhibits alinear and ohmic I-V characteristic. This indicates that metallicelectron conduction characteristics are realized because highly pure Cucurrent paths are formed so as to penetrate the oxide layer in thespacer. In FIG. 10B, the resistance R increases slightly with increasingvoltage V because of Joule heat. The abrupt drop of the resistance Rnear V=310 mV shown in FIG. 10B is due to structural failure of theCCP-NOL.

FIGS. 11A and 11B show the I-V and R-V characteristics, respectively, ofan element produced by performing the PIT and IAO process to the secondmetal layer (AlCu) without forming the first metal layer (Cu layer).FIG. 11B shows the tunnel conduction characteristics that resistancedecreases with increasing voltage. Also, FIG. 11A shows poor linearityof the I-V characteristics. These results indicate that, if the firstmetal layer (Cu layer) is not formed, no Cu current paths are formedeven with the PIT and IAO process, resulting in an element similar to aTMR (tunneling magnetoresistance) element. The reason why voltage dropsabruptly at I=1.5 mA in FIG. 11A is due to dielectric breakdown of thetunnel barrier layer.

In order to form a spacer layer 16 having a good insulating portion andhigh-purity current paths with a low ρ_(Cu) value, an ion-beam treatmentmay be further performed after the PIT/IAO treatments. This treatment isreferred to as an AIT (after ion treatment) relative to the PIT (pre-iontreatment). The AIT aims at following two effects: (1) When the IAO isperformed, CuO is generated by oxidation of Cu in the IAO and remainsafter the IAO. The particular ion-beam treatment (AIT) can reduce CuOback to Cu, making it possible to improve the purity of the metal pathsand to raise the MR ratio. (2) In the spacer layer, Al₂O₃ and Cu are notcompletely separated after the IAO. The particular ion-beam treatment(AIT) can enhance the separation of Al₂O₃ and Cu. The beam conditionsfor the AIT can be similar to those conditions either for the PIT or theIAO. AIT can be performed using RF plasma instead of an ion beam.Further, if the AIT conditions are optimized, it may be possible toprovide a high MR ratio by only performing the IAO and AIT processeswithout performing the PIT process. In this case, it is preferable toperform the oxidation by the IAO not the natural oxidation in order toprovide a high MR ratio as the case described above. However, thenatural oxidation can be used in some cases. If the AIT is performedunder intense beam conditions, the surface of the sample may beroughened, which may increase an interlayer coupling field H_(in)between the pinned layer and the free layer. Therefore, it is necessaryto optimize the beam conditions for the AIT.

Example 3

In the present Example, materials advantageous for achieving a high MRratio in a CCP-CPP element manufactured by the method according to thepresent invention will be described. Specifically, Co₉₀Fe₁₀ or Fe₅₀Co₅₀was used as a material for the magnetic layers provided over and underthe spacer layer. The layers in the CCP-CPP element from the underlayerto the cap layer are as follows:

underlayer: Ta [5 nm]/Ru [2 nm],

pinning layer: PtMn [15 nm],

pinned layer: Co₉₀Fe₁₀ [4 nm]/Ru [0.9 nm]/“Mag” [4 nm],

metal layer: Cu [2.5 nm],

spacer layer: Al₂O₃ insulating layer and Cu current paths 21 (preparedby depositing Al₉₀Cu₁₀ [x nm], followed by performing PIT and IAOtreatment),

metal layer: Cu [2.5 nm], and

free layer: “Mag” [4 nm].

In the present example, Co₉₀Fe₁₀ or Fe₅₀Co₅₀ was used as a magneticlayer denoted as “Mag”. FIG. 12 shows evaluations of the characteristicsof these CCP-CPP elements. FIG. 12 also shows the results of fittingbased on the Valet-Fert model described in Example 2.

As is apparent from FIG. 12, the use of Fe₅₀Co₅₀ as the magnetic layersincreases the MR ratio compared to the use of Co₉₀Fe₁₀. In FIG. 12,measured data agrees well with the results of the fitting based on theValet-Fert model. The improvement of the MR ratio can be interpreted bythe fact that the interface scattering rate γ of FeCo, 0.72, is largerthan that of CoFe, 0.62. The γ values were derived from experiments formetal CCP elements including a spacer layer made of Cu [5 nm] (see H.Yuasa et al, J. Appl. Phys., 92, 2646 (2003)). Therefore, in order toachieve a high MR ratio in the CCP-CPP element, it is particularlyimportant to use a magnetic material with a high interface scatteringrate γ. More specifically, in a case of the CCP-CPP element having theCCP structure, the interface resistance between the spacer layer and themagnetic layer greatly contributes the total element resistance, so thatthe influence of the interface scattering rate γ to the MR ratio becomesremarkably large compared to the case of the CPP element without the CCPstructure. A preferable magnetic material with a high interfacescattering rate γ is, for example, Fe₅₀Co₅₀, which has a compositionexpressed by Fe_(x)Co_(100-x) (x=30 to 100%) of a bcc structure.

In the present example, the ρ_(Cu) values (75 μΩcm) are equivalentregardless of the type of the magnetic materials. Accordingly, there issubstantially no difference in the purity of the current paths betweentwo elements. This is because the present example uses the same PIT andIAO conditions regardless of which of the magnetic materials is used forthe element. On the other hand, ρ_(Cu) in the present example, 75 μΩcm,is larger than that in Example 2, 65 μΩcm, indicating slightly poorpurity of the current paths. This is due to difference in PIT and IAOconditions between the present example and Example 2.

(Application)

Application of the magnetoresistive element (CCP-CPP element) accordingto the embodiments of the present invention will be described below.

In the embodiments of the present invention, the RA of the CPP elementis preferably set to 500 mΩμm² or less, more preferably 300 mΩμm² orless, in view of achieving higher density. The element resistance RA iscalculated by multiplying the resistance R of the CPP element by theeffective area A of a conductive part of the spin-valve film. In thiscase, the resistance R can be directly measured and easily determined.On the other hand, the effective area A of the conductive part of thespin-valve film has a value dependent on the element structure.Accordingly, attention must be paid to determination the effective areaA.

For example, if the entire spin-valve film is patterned as aneffectively sensing part, the effective area A is the area of the entirespin-valve film. In this case, the area of the spin valve film is set to0.04 μm² or less so as to set an appropriate resistance. For a recordingdensity of 200 Gbpsi or more, the area of the spin valve film is set to0.02 μm² or less.

If a lower or upper electrode having a smaller area than the spin-valvefilm is formed in contact with the spin-valve film, however, theeffective area A is the area of the lower or upper electrode. If thelower and upper electrodes have different areas, the area of the smallerelectrode is the effective area A of the spin-valve film. In this case,the area of the smaller electrode is set to 0.04 μm² or less so as toset an appropriate resistance.

An example of determining the effective area A will be described withreference to FIGS. 13 and 14, which will be described in more detaillater. The smallest area of the spin-valve film 10 shown in FIG. 13 isthat of a part where the film 10 is in contact with the upper electrode20. The width of this part is considered as the track width Tw. Thesmallest height of the spin-valve film 10 shown in FIG. 14 is also thatof a part where the film 10 is in contact with the upper electrode 20.The height of this part is considered as the height length D. In thiscase, the effective area A is determined as: A=Tw×D.

In the magnetoresistive element according to the embodiment of thepresent invention, the resistance R between the electrodes can be set to100 Ω or less. The resistance R is a value measured, for example,between two electrode pads in a read head installed to the tip of a headgimbal assembly (HGA).

The magnetoresistive element according to the embodiment of the presentinvention desirably has an fcc (111) orientation if the pinned layer orfree layer has the fcc structure. The magnetoresistive element desirablyhas a bcc (110) orientation if the pinned layer or free layer has thebcc structure. The magnetoresistive element desirably has an hcp (001)or (110) orientation if the pinned layer or free layer has the hcpstructure.

The crystal orientation of the magnetoresistive element according to theembodiment of the present invention preferably has a dispersion angle of4.0° or less, more preferably 3.5° or less, still more preferably 3.0°or less. This value is obtained by measuring a full width at halfmaximum of a rocking curve at a peak position obtained by θ-2θmeasurement in X-ray diffraction. In a magnetic head, this value can bedetected as a dispersion angle of a nano-diffraction spot in a crosssection. Although depending on the material for the antiferromagneticfilm, the lattice spacing of the antiferromagnetic film is generallydifferent from that of the pinned layer, spacer layer, and free layer.Consequently, the orientation dispersion angle can be separatelycalculated for each layer. For example, the lattice spacing of platinummanganese (PtMn) is often different from that of the pinned layer,spacer layer, and free layer. Since the platinum manganese (PtMn) ismade in a relatively thick film, it is a suitable material for measuringdispersion in crystal orientation. For the pinned layer, spacer layer,and free layer, the pinned layer and the free layer may have differentcrystal structures such as the bcc and fcc structures. Consequently, thepinned layer and the free layer have different crystal orientationdispersion angles.

(Embodiments of Magnetic Head)

FIGS. 13 and 14 show the magnetoresistive element according to theembodiment of the present invention which is incorporated in a magnetichead. FIG. 13 is a cross-sectional view of the magnetoresistive elementtaken along a direction substantially parallel to the air bearingsurface facing a magnetic recording media (not shown). FIG. 14 is across-sectional view of the magnetoresistive element taken along adirection perpendicular to the air bearing surface (ABS).

The magnetic head shown in FIGS. 13 and 14 have a so-called hard abuttedstructure. The magnetoresistive film 10 is an aforementioned CCP-CPPfilm. The lower electrode 11 and the upper electrode 20 are providedunder and over the magnetoresistive film 10, respectively. In FIG. 13,bias field application films 41 and insulating films 42 are stacked onthe both sides of the magnetoresistive film 10. As shown in FIG. 14, aprotective layer 43 is provided in the air bearing surface of themagnetoresistive film 10.

A sense current for the magnetoresistive film 10 is supplied by theelectrodes 11 and 20 perpendicularly to the plane as shown by arrow A,the electrodes 11 and 20 being arranged under and over themagnetoresistive film 10. Further, the pair of bias field applicationfilms 41, 41, provided on the both sides of the magnetoresistive film10, applies a bias field to the magnetoresistive film 10. The bias fieldcontrols the magnetic anisotropy of the free layer in themagnetoresistive film 10 to make the free layer into a single domain.This stabilizes the domain structure of the free layer. It is thuspossible to suppress Barkhausen noise associated with movement ofmagnetic domain walls.

The present invention improves the MR ratio of the magnetoresistiveelement. Accordingly, the application of the present invention to amagnetic head enables sensitive magnetic reproduction.

(Embodiments of Hard Disk and Head Gimbal Assembly)

The magnetic head shown in FIGS. 13 and 14 may be incorporated in aread/write integrated magnetic head assembly, which can then be mountedin a magnetic recording apparatus.

FIG. 15 is a perspective view schematically showing the configuration ofa major portion of such a magnetic recording apparatus. A magneticrecording apparatus 150 is of a type using a rotary actuator. In thisfigure, a magnetic disk 200 is installed on a spindle 152. The magneticdisk 200 is rotated in the direction of arrow A by a motor (not shown)that responds to control signals from a drive controller (not shown).The magnetic recording apparatus 150 according to the present inventionmay comprise a plurality of disks 200.

A head slider 153 is attached to the tip of a suspension 154 to readfrom and write to the magnetic disk 200. The head slider 153 has amagnetic head mounted near the tip thereof and including themagnetoresistive element according to any of the above embodiments.

When the magnetic disk 200 rotates, the air bearing surface (ABS) ofhead slider 153 is held so as to float on the surface of the magneticdisk 200 by a predetermined height. The head slider 153 may be of aso-called in-contact type contacting to the magnetic disk 200.

The suspension 154 is connected to one end of an actuator arm 155. Avoice coil motor 156, a kind of linear motor, is provided on the otherend of the actuator arm 155. The voice coil motor 156 forms a magneticcircuit including a driving coil (not shown) wound around a bobbin and apermanent magnet and a counter yoke arranged opposite each other so asto sandwich the coil therebetween.

The actuator arm 155 is held by ball bearings (not shown) provided attwo vertical positions of the pivot 157. The actuator arm 155 can berotatably slid by the voice coil motor 156.

FIG. 16 is an enlarged perspective view of a part of the head gimbalassembly including tip end side of the actuator arm 155, which is viewedfrom the disk. The assembly 160 has the actuator arm 155, and thesuspension 154 is connected to one end of the actuator arm 155. The headslider 153 is attached to the tip of the suspension 154, and the headslider 153 comprises a magnetic head including the magnetoresistiveelement according to any of the above embodiments. The suspension 154has leads 164 used to write and read signals. The leads 164 areelectrically connected to respective electrodes in the magnetic headincorporated in the head slider 153. Reference numeral 165 in the figuredenotes electrode pads of the assembly 160.

The present invention comprises the magnetic head including themagnetoresistive element according to any of the above embodiments ofthe present invention. This makes it possible to reliably readinformation magnetically recorded on the magnetic disk 200 at arecording density higher than that in the prior art.

(Embodiments of Magnetic Memory)

A magnetic memory using the magnetoresistive element according to anembodiment of the present invention will now be described. That is, themagnetoresistive element according to any of the above embodiments ofthe present invention makes it possible to provide a magnetic memory,for example, a magnetic random access memory (MRAM) in which memorycells are arrayed in a matrix.

FIG. 17 is a diagram showing an example of the matrix configuration of amagnetic memory according to an embodiment of the present invention.This figure shows the circuit configuration in which memory cells arearrayed. The magnetic memory comprises a column decoder 350 and a rowdecoder 351 to select one bit in the array. A bit line 334 and a wordline 332 are used to turn on and uniquely select a switching transistor330. Detection by a sense amplifier 352 enables reading of the bitinformation recorded in the magnetic recording layer (free layer) in themagnetoresistive element 10. To write bit information, a current ispassed through a particular word line 323 and a particular bit line 322to generate a magnetic field to be applied.

FIG. 18 is a diagram showing another example of the matrix configurationof a magnetic memory according to an embodiment of the presentinvention. In this case, one of bit lines 322 is selected by a decoder361, while one of the word lines 334 is selected by a decoder 360; thebit lines 322 and the word lines 334 are arrayed in a matrix. Thus, aparticular memory cell in the array is selected. Each memory cell has astructure in which the magnetoresistive element 10 and a diode D areconnected in series. Here, the diode D serves to prevent a sense currentfrom bypassing in the memory cells except the selected magnetoresistiveelement 10. A write operation is performed by using a magnetic fieldgenerated by passing a write current through each of a particular bitline 322 and a particular word line 323.

FIG. 19 is a cross-sectional view showing a major portion of a magneticmemory according to an embodiment of the present invention. FIG. 20 is across-sectional view taken along the line A-A′ in FIG. 19. The structureshown in these figures corresponds to a memory cell for one bit includedin the magnetic memory shown in FIG. 17 or 18. The memory cell has astorage element 311 and an address selecting transistor 312.

The storage element 311 has the magnetoresistive element 10 and a pairof wires 322 and 324 connected to the magnetoresistive element 10. Themagnetoresistive element 10 is any CCP-CPP element of the aboveembodiments.

On the other hand, the selecting transistor 312 is provided with atransistor 330 connected to the magnetoresistive element 10 through vias326 and buried wires 328. The transistor 330 performs a switchingoperation in accordance with a voltage applied to a gate 332 tocontrollably open and close the current paths between themagnetoresistive element 10 and a wire 334.

A write wire 323 is provided below the magnetoresistive element 10 in adirection orthogonal to the wire 322. The write wires 322 and 323 can beformed of, for example, aluminum (Al), copper (Cu), tungsten (W),tantalum (Ta), or an alloy of these elements.

In the memory configured as described above, to write bit information tothe magnetoresistive element 10, a write pulse current is passed throughthe wires 322 and 323 to induce a synthetic field. The synthetic fieldis applied to appropriately reverse the magnetization of the recordinglayer of the magnetoresistive element.

Further, to read bit information, a sense current is passed through thewire 322, the magnetoresistive element 10 including the magneticrecording layer, and the lower electrode 324. Then, the resistance valueor a resistance change of the magnetoresistive element 10 is measured.

The magnetic memory according to the embodiment of the present inventionuses the magnetoresistive element (CCP-CPP element) according to any ofthe above embodiments. Consequently, even with a reduction in cell size,the magnetic domains in the recording layer are surely controlled toallow write and read operations to be reliably performed.

The embodiments of the present invention have been described withreference to the specific examples. However, the present invention isnot limited to these specific examples. For example, for the specificstructure of the magnetoresistive element as well as the shapes andmaterials of the electrodes, bias application film, insulating film, andthe like, those skilled in the art can similarly implement the presentinvention to produce similar effects by making appropriate selectionsfrom the corresponding well-known ranges.

For example, when the magnetoresistive element is applied to a readmagnetic head, the detection resolution of the magnetic head can bedefined by providing magnetic shields on both sides of the element.

Further, the present invention can be applied to a magnetic head ormagnetic recording apparatus based on a perpendicular magnetic recordingsystem as well as a longitudinal magnetic recording system, and canproduce similar effects in any system.

Moreover, the magnetic recording apparatus according to the presentinvention may be a so-called a rigid type constantly provided withparticular recording media or a removable type that allows recordingmedia to be exchanged.

The scope of the present invention also includes all themagnetoresistive elements, magnetic heads, magnetic recordingapparatuses, and magnetic memories that can be implemented by thoseskilled in the art by appropriately changing the designs of the abovemagnetic heads and magnetic recording apparatuses described above as theembodiments of the present invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method for manufacturing a magnetoresistive element including amagnetization pinned layer having a magnetization directionsubstantially pinned in one direction, a magnetization free layer havinga magnetization direction that varies depending on an external field,and a spacer layer including an insulating layer provided between themagnetization pinned layer and the magnetization free layer and currentpaths penetrating into the insulating layer, the method comprising: aprocess of forming the spacer layer comprising: depositing a first metallayer including a first element; depositing a second metal layerincluding a second element that is more easily oxidized than the firstelement on the first metal layer; performing a pretreatment ofirradiating the second metal layer with an ion beam or a RF plasma of arare gas so as to cause the first element in the first metal layer to besucked up in the second metal layer as the current paths; and supplyingan oxidation gas or a nitriding gas while irradiating the second metallayer with an ion beam or a RF plasma of a rare gas so as to form theinsulating layer.
 2. The method according to claim 1, wherein the firstmetal layer includes at least one element selected from the groupconsisting of Cu, Au, and Ag.
 3. The method according to claim 1,wherein the second metal layer consists of at least one element selectedfrom the group consisting of Al, Si, Hf, Ti, Ta, Mo, W, Nb, Mg, Cr, andZr.
 4. The method according to claim 1, wherein the pretreatment isperformed with an acceleration voltage for the ion beam or the RF plasmaof the rare gas setting to 30 V or more and 130 V or less.
 5. The methodaccording to claim 1, wherein the pretreatment is performed with anacceleration voltage for the ion beam or the RF plasma of the rare gassetting to 40V or more and 60 V or less.
 6. The method according toclaim 1, wherein the first metal layer has a thickness of 0.1 nm or moreand 1 nm or less.
 7. The method according to claim 1, wherein theinsulating layer is an oxide or a nitride including at least one elementselected from the group consisting of Al, Si, Hf, Ti, Ta, Mo, W, Nb, Mg,Cr, and Zr.
 8. The method according to claim 1, wherein the second metallayer has a thickness of 0.5 nm or more and 2 nm or less.
 9. The methodaccording to claim 1, wherein the current paths have a diameter of 2 nmor more and 6 nm or less.
 10. The method according to claim 1, whereinthe magnetization pinned layer has a body-centered cubic structure at aninterface with the spacer layer.
 11. The method according to claim 1,wherein the magnetization pinned layer comprises a FexCo100-x alloylayer, whereby x≧30 atomic %.
 12. The method according to claim 1,further comprising: forming a Cu layer on the spacer layer.
 13. Themethod according to claim 12, wherein the Cu layer has a thickness of0.1 nm or more and 0.5 nm or less.
 14. A method for manufacturing amagnetoresistive element including a magnetization pinned layer having amagnetization direction substantially pinned in one direction, amagnetization free layer having a magnetization direction that variesdepending on an external field, and a spacer layer including aninsulating layer provided between the magnetization pinned layer and themagnetization free layer and current paths penetrating into theinsulating layer, the method comprising: a process of forming the spacerlayer comprising: depositing a first metal layer including a firstelement; depositing a second metal layer consisting of one secondelement selected from the group consisting of Al, Si, Hf, Ti, Ta, Mo, W,Nb, Mg, Cr, and Zr on the first metal layer, the second element beingmore easily oxidized than the first element; performing a pretreatmentof irradiating the second metal layer with an ion beam or a RF plasma ofa rare gas so as to cause the first element in the first metal layer tobe sucked up in the second metal layer as the current paths; andsupplying an oxidation gas or a nitriding gas while irradiating thesecond metal layer with an ion beam or a RF plasma of a rare gas so asto form the insulating layer.
 15. The method according to claim 14,wherein the first metal layer includes one element selected from thegroup consisting of Cu, Au, and Ag.
 16. the method according to claim14, wherein the pretreatment is performed with an acceleration voltagefor the ion beam or the RF plasma of the rare gas setting to 30 V ormore and 130 V or less.
 17. The method according to claim 14, whereinthe pretreatment is performed with an acceleration voltage for the ionbeam or the RF plasma of the rare gas setting to 40V or more and 60 V orless.
 18. The method according to claim 14, wherein the first metallayer has a thickness of 0.1 nm or more and 1 nm or less.
 19. The methodaccording to claim 14, wherein the insulating layer is an oxide or anitride including at least one element selected from the groupconsisting of Al, Si, Hf, Ti, Ta, Mo, W, Nb, Mg, Cr, and Zr.
 20. Themethod according to claim 14, wherein the second metal layer has athickness of 0.5 nm or more and 2 nm or less.
 21. The method accordingto claim 14, wherein the current paths have a diameter of 2 nm or moreand 6 nm or less.
 22. The method according to claim 14, wherein themagnetization pinned layer has a body-centered cubic structure at aninterface with the spacer layer.
 23. The method according to claim 14,wherein the magnetization pinned layer comprises a FexCo100-x alloylayer, whereby x≧30 atomic %.
 24. The method according to claim 14,further comprising: forming a Cu layer on the spacer layer.
 25. Themethod according to claim 14, wherein the Cu layer has a thickness of0.1 nm or more and 0.5 nm or less.